Physiological activating substances are produced and secreted at trace amounts in the human body and play an essential role in various metabolisms and modulations. The physiological activating substances known to date include insulin, interleukins, hemopoietic growth regulating factors, such as stem cell factor, granulocyte colony stimulating factor, erythropoietin, etc, and are too numerous to describe their great functions in the human body, in detail. The reason why such physiological activating substances, in spite of their importance, have not yet been industrialized, is that they are difficult to isolate and purify owing to their trace amount in the human body. Further, the physiological activating substances produced by using a procaryotic expression system, such as that obtained from E. coli, frequently do not perform their normal functions in the human body as well as have not yet overcome the safety problem which must be solved before administration.
According to the reports contributed to the academic circles, it is known that, even if there is used a promotor site for a gene which is expressed specifically in a mammary gland tissue, the expression level is different depending on the species from which the promotor is obtained and on the genes to be expressed (Clark et al. (1987) Trends Biotech. 5, 20–24; Simons et al., (1987) Nature 328, 530–532; Lee at al., (1988) Nucl. Acids Res. 16, 1027–1041; Vilotte et al., (1988) Eur. J. Biochem. 186, 43–48; Gorden et al., (1987) Bio/Technology 8, 443–446; Shani et al., (1992) Transgenic Res. 1, 195–208; Wright et al., (1991) Bio/Technology 9, 830–834; Ebert et al., (1991) Bio/Technology 9, 835–838; Mega et al., (1994) Transgenic Res. 3, 36–42; Wei et al., (1995) Transgenic Res. 4, 232–240; Gutierrez et al., (1996) Transgenic Res. 5 271–279)
In order to produce physiological activating substances, the expression systems which take advantage of E. coli (Korean Pat. Publication No. 94-5585) and animal cells have been usually used. These techniques would occasionally bring about industrial successes, but still have significant problems to be solved. For instance, in the case of the expression utilizing E. coli, mass production is possible with low cost. However, since E. coli, a prokaryote, does not perform a posttranslational modification, which is a feature of eukaryotes, such a human physiological activating substance as EPO cannot exert its activity if it is produced in E. coli. To avoid this problem, active research has been and continues to be directed to the development expression systems which take advantage of animal cells. The products expressed in these systems are active in the human body because they experience posttranslational modifications. However, the problem of high cost for culturing animal cells remains unsolved.
Almost all of the physiological activating substances that are industrially produced utilize the above mentioned techniques, so they have the problems to be solved, including activity sustenance, cost, and isolation and purification.